A cochlear implant (CI) is a surgically implanted electronic device that provides a perception of sound to a person having a hearing impairment. In some people, cochlear implants may enable sufficient hearing for better understanding of speech. The quality of sound is different from natural hearing, with less sound information being received and processed by the brain.
Implanting both cochleas of hearing-impaired listeners with cochlear implants (referred to as bilateral cochlear implants) has become more common in recent years. Using binaural hearing in normal hearing listeners, i.e. where input along the auditory pathway after both ears are presented with the sound are integrated, boosts a person's ability to focus on speech in noisy situations, and allows a person to tune into sounds that are even low in level compared with the competing noise. There is thus a need for an effective system and method for providing these binaural benefits to hearing-impaired subjects, such as those subject that have bilateral cochlear implants.
Improving quality of life for CI users such as by prioritizing improving speech intelligibility in noise, sound localization, and pitch discrimination may require new types of information to be sent to and output by the CI implant.
One such new type of information that would help the CI users are binaural cues, i.e. synchronized information between the two ears. There are two main binaural cues for localizing sound in a plane of azimuth, i.e. angle of a sound source on the horizon relative to a point in the center of the head between the ears, namely (i) interaural time differences (ITDs), and (ii) interaural level differences (ILDs). ILDs are primarily a high-frequency cue, and occur because the listener's head shadowing the sound at the ear contralateral with respect to a sound source. Acoustically ITDs exist at all frequencies, however, normal hearing humans are typically most sensitive to ITDs at 500-900 Hz. In existing cochlear implant systems, the ITDs are not well-coded. It is expected that including such timing information will enhance spatial sound perception.
In an auditory environment (auditory scene) containing one or more sound sources (talkers or other sources of sound), individuals with normal hearing can utilize the binaural cues along with neural machinery for sound localization and to improve speech intelligibility in an auditory scene. One such auditory scene may include a talker (referred to as a target) spatially separated from a second talker (referred to as a masker), such as in the well-known “cocktail-party” problem.
Two normally functioning ears enable the human isolating spatially separated sources into different ‘sound objects.’ Consequently, normal hearing listeners can leverage this spatial separation to improve their speech reception of a target talker, provided that the competing noise sources are spatially separated from the target. Such an improvement in speech intelligibility is referred to in the art as a spatial release from masking (SRM).
Bilateral CI systems that aim to introduce this extra information need to develop a processing strategy that preserves or introduces this information appropriately and must also find a way to efficiently transmit this information to the implant system, for example utilizing transcutaneous data links. The data transmission problem is not a trivial one. In a bilateral system, the number of electrodes to command is doubled vs. a similar monaural system and extra information about the relationship between the two ears must be sent. Additionally, timing between the two electrode arrays need to be synchronized. Therefore, an efficient way to encode the synchronized ITD/timing data for both devices of a bilateral cochlear implant is needed. Reducing the amount of data to code this information will enable the data to be sent within the bandwidth budget of a transcutaneous data link and deliver an acceptable battery life for the patient.